Discrete electronic components such as chip carriers are mounted on printed circuit boards by means of some type of soldering process. When such components need to be surface mounted (as opposed to inserted through holes in the board), a soldering technique utilizing solder reflow machines is introduced after the chip carriers have been mounted. Such machines blow hot air, at the solder melting temperature, via nozzles onto the top surface of the boards in order to smooth any globs or excess accumulations of solder. The reflow machines continue to heat the boards for a period of approximately 40 seconds.
It is during and after this reflow stage that a printed circuit board will experience internal heat stresses and undergo warping caused by the rapid temperature change due to the sudden exposure to the hot air and subsequent cooling. Before positioning and soldering a chip carrier onto the surface of a printed circuit board, the board must be preheated in order to prevent such warping.
Presently, the board is not uniformly heated since component leads, protruding from the lower surface of the board, do not permit the board to sit flat on the heating surface. Therefore, warping still occurs in the local areas of the board which were not heated properly. Secondly, the nozzle of a reflow machine, which makes contact with the printed circuit board during reflow, will not discharge hot air evenly upon the boards if it does not sit flat and is tilted in some manner.